Often, the production of semiconductor devices, displays, photovoltaics, etc. involves, for example, plasma etching. Plasma etching is a form of plasma processing of semiconductor material and is often used to fabricate integrated circuits. Plasma etching typically involves the generation of a glow discharge (i.e., plasma) by application of radio-frequency or microwave power in means familiar to one skilled in the art. Ions, neutral and exited atoms from the plasma are applied to the wafer.
During the process, the plasma generates volatile etch products from the chemical reactions between the elements of the material etched and the reactive species generated by the plasma.
In plasma processing, the chemistry of the plasma strongly affects the processing rate. This is particularly true about the local chemistry of the plasma. The local chemistry of the plasma is the local concentrations of various chemical species in the plasma environment proximate the substrate being processed. Certain species, particularly transient chemical species, such as radicals have a great influence on the plasma processing outcome. It is known that elevated local concentrations of these species can produce areas of faster or slower processing, which may lead to inconsistencies in the production and ultimately in the devices being produced.
The chemistry of a plasma process is controlled in a direct or indirect manner through the control of a large number of process variables. Examples of such variables includes one or more RF or microwave powers supplied to excite the plasma, the gas flows and kinds of gases supplied to the plasma processing chamber, the pressure in the plasma processing chamber, the type of substrate being processed, the pumping speed delivered to the plasma processing chamber, and many more.
Optical emission spectroscopy (OES) has proven itself as a useful tool for process development and monitoring in plasma processing. In OES, the presence and concentrations of certain chemical species of particular interest, such as radicals, is deduced from acquired optical (i.e. light) emission spectra of the plasma, wherein the intensities of certain spectral lines and ratios thereof correlate to the concentrations of chemical species.
OES is usually done by acquiring optical emission spectra from a single elongated volume (i.e., “ray”) within the plasma that is inside the plasma processing chamber. The collection of the optical emission signals inherently results in averaging of the plasma optical emission spectra along the length of this elongated volume and thus all the information about local variations of the plasma optical emission spectra. As a result, all local variations of chemical species concentrations are generally lost.
The Detailed Description references the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.